The Voyager mission was officially approved in May 1972, has received
the dedicated efforts of many skilled personnel for over two decades,
and has returned more new knowledge about the outer planets than
had existed in all of the preceding history of astronomy and planetary
science. And the two Voyager machines are still performing like
- The total cost of the Voyager mission from May 1972 through the
Neptune encounter (including launch vehicles, nuclear-power-source
RTGs, and DSN tracking support) is 865 million dollars. At first, this
may sound very expensive, but the fantastic returns are a
bargain when we place the costs in the proper perspective. It is
important to realize that:
- on a per-capita basis, this is only 20 cents per U.S. resident per
year, or roughly half the cost of one candy bar each year since project
- the daily interest on the U.S. national debt is a major fraction of
the entire cost of Voyager.
- A total of 11,000 workyears will have been devoted to the Voyager
project through the Neptune encounter. This is equivalent to one-third
the amount of effort estimated to complete the great pyramid
at Giza to King Cheops.
- A total of five trillion bits of scientific data will have
been returned to Earth by both Voyager spacecraft at the completion
of the Neptune encounter. This represents enough bits to encode
over 6000 complete sets of the Encyclopedia Brittanica, and is
equivalent to about 1000 bits of information provided to each
person on Earth.
- The sensitivity of our deep-space tracking antennas located
around the world is truly amazing. The antennas must capture Voyager
information from a signal so weak that the power striking the
antenna is only 10 exponent -16 watts (1 part in 10 quadrillion). A
electronic digital watch operates at a power level 20 billion
times greater than this feeble level.
- Each Voyager spacecraft comprises 65,000 individual parts. Many of
these parts have a large number of "equivalent"
smaller parts such as transistors. One computer memory alone contains
over one million equivalent electronic parts, with each spacecraft
containing some five million equivalent parts. Since a color TV set
contains about 2500 equivalent parts, each Voyager has the
equivalent electronic circuit complexity of some 2000 color TV sets.
- Like the HAL computer aboard the ship Discovery from the famous
science fiction story 2001: A Space Odyssey, each Voyager
is equipped with computer programming for autonomous fault protection.
The Voyager system is one of the most sophisticated ever designed
for a deep-space probe. There are seven top-level fault protection
routines, each capable of covering a multitude of possible failures.
The spacecraft can place itself in a safe state in a matter of only
seconds or minutes, an ability that is critical for its survival
when round-trip communication times for Earth stretch to several hours
as the spacecraft journeys to the remote outer solar system.
- Both Voyagers were specifically designed and protected to withstand
the large radiation dosage during the Jupiter swing-by. This was
accomplished by selecting radiation-hardened parts and by shielding very
sensitive parts. An unprotected human passenger riding aboard
Voyager 1 during its Jupiter encounter would have received a radiation
dose equal to one thousand times the lethal level.
- The Voyager spacecraft can point its scientific instruments on the
scan platform to an accuracy of better than one-tenth of
a degree. This is comparable to bowling strike-after-strike ad
infinitum, assuming that you must hit within one inch of the
strike pocket every time. Such precision is necessary to properly center
the narrow-angle picture whose square field-of-view would
be equivalent to the width of a bowling pin.
- To avoid smearing in Voyager's television pictures, spacecraft
angular rates must be extremely small to hold the cameras as steady
as possible during the exposure time. Each spacecraft is so steady that
angular rates are typically 15 times slower than the motion
of a clock's hour hand. But even this will not be quite steady enough at
Neptune, where light levels are 900 times fainter than
those on Earth. Spacecraft engineers have already devised ways to make
Voyager 30 times steadier than the hour hand on a clock.
- The electronics and heaters aboard each nearly one-ton Voyager
spacecraft can operate on only 400 watts of power, or roughly
one-fourth that used by an average residential home in the western
- A set of small thrusters provides Voyager with the capability for
attitude control and trajectory correction. Each of these
tiny assemblies has a thrust of only three ounces. In the absence of
friction, on a level road, it would take nearly six hours to
accelerate a large car up to a speed of 48 km/h (30 mph) using one of
- The Voyager scan platform can be moved about two axes of rotation.
A thumb-sized motor in the gear train drive assembly (which turns
9000 revolutions for each single revolution of the scan platform) will
have rotated five million revolutions from launch through
the Neptune encounter. This is equivalent to the number of automobile
crankshaft revolutions during a trip of 2725 km (1700 mi).
- The Voyager gyroscopes can detect spacecraft angular motion as
little as one ten-thousandth of a degree. The Sun's apparent
motion in our sky moves over 40 times that amount in just one second.
- The tape recorder aboard each Voyager has been designed to record
and playback a great deal of scientific data. The tape
head should not begin to wear out until the tape has been moved back and
forth through a distance comparable to that across the
United States. Imagine playing a two-hour video cassette on your home
VCR once a day for the next 22 years, without a failure.
- The Voyager magnetometers are mounted on a frail, spindly,
fiberglass boom that was unfurled from a two-foot-long can shortly
after the spacecraft left Earth. After the boom telescoped and rotated
out of the can to an extension of nearly 13 meters (43
feet), the orientations of the magnetometer sensors were controlled to
an accuracy better than two degrees.
- Each Voyager used the enormous gravity field of Jupiter to
be hurled on to Saturn, experiencing a Sun-relative speed increase
of roughly 35,700 mph. As total energy within the solar system
must be conserved, Jupiter was initially slowed in its solar orbit---but
by only one foot per trillion years. Additional gravity-assist
swing-bys of Saturn and Uranus were necessary for Voyager 2 to
complete its Grand Tour flight to Neptune, reducing the trip time
by nearly twenty years when compared to the unassisted Earth-to-Neptune
- The Voyager delivery accuracy at Neptune of 100 km (62 mi),
divided by the trip distance or arc length traveled of 7,128,603,456
km (4,429,508,700 mi), is equivalent to the feat of sinking a
3630 km (2260 mi) golf putt, assuming that the golfer can make
a few illegal fine adjustments while the ball is rolling across
this incredibly long green.
- Voyager's fuel efficiency (in terms of mpg) is quite impressive.
Even though most of the launch vehicle's 700 ton weight is due
to rocket fuel, Voyager 2's great travel distance of 7.1 billion
km (4.4 billion mi) from launch to Neptune results in a fuel economy
of about 13,000 km per liter (30,000 mi per gallon). As Voyager
2 streaks by Neptune and coasts out of the solar system, this
economy will get better and better!
- The resolution of the Voyager narrow-angle television cameras
is sharp enough to read a newspaper headline at a distance of
1 km (0.62 mi).
- Pele, the largest of the volcanoes seen on Jupiter's moon Io,
is throwing sulfur and sulfur-dioxide products to heights 30 times
that of Mount Everest, and the fallout zone covers an area the
size of France. The eruption of Mount St. Helens was but a tiny
hiccup in comparison (admittedly, Io's surface-level gravity is
some six times weaker than that of Earth).
- The smooth water-ice surface of Jupiter's moon Europa may hide
an ocean beneath, but some scientists believe any past oceans
have turned to slush or ice. In 2010: Odyssey Two, Arthur
C. Clarke wraps his story around the possibility of life developing
within the oceans of Europa.
- The rings of Saturn appeared to the Voyagers as a dazzling
necklace of 10,000 strands. Trillions of ice particles and car-sized
bergs race along each of the million-kilometer-long tracks, with
the traffic flow orchestrated by the combined gravitational tugs
of Saturn, a retinue of moons and moonlets, and even nearby ring
particles. The rings of Saturn are so thin in proportion to their
171,000 km (106,000 mi) width that, if a full-scale model were
to be built with the thickness of a phonograph record the model
would have to measure four miles from its inner edge to its outer
rim. An intricate tapestry of right-article patterns is created
by many complex dynamic interactions that have spawned new theories
of wave and particle motion.
- Saturn's largest moon Titan was seen as a strange world with
its dense atmosphere and variety of hydrocarbons that slowly fall
upon seas of ethane and methane. To some scientists, Titan, with
its principally nitrogen atmosphere, seemed like a small Earth
whose evolution had long ago been halted by the arrival of its
ice age, perhaps deep-freezing a few organic relics beneath its
- The rings of Uranus are so dark that Voyager's challenge of
taking their picture was comparable to the task of photographing
a pile of charcoal briquettes at the foot of a Christmas tree,
illuminated only by a 1 watt bulb at the top of the tree, using
ASA-64 film. And Neptune light levels will be less than half those
- The solar system does not end at the orbit of Pluto, the ninth
planet. Nor does it end at the heliopause boundary, where the
solar wind can no longer continue to expand outward against the
interstellar wind. It extends over a thousand times farther out
where a swarm of small cometary nuclei, termed Oort's Cloud, is
barely held in orbit by the Sun's gravity, feeble at such a great
distance. Voyager 1 passed above the orbit of Pluto in May 1988,
and Voyager 2 will pass beneath Pluto's orbit in august 1990.
But even at speeds of over 35,000 mph, it will take nearly 20,000
years for the Voyagers to reach the middle of the comet swarm,
and possibly twice this long for them to pass the outer boundaries
of cometary space. By this time, they will have traveled a distance
of two light-years, equivalent to half of the distance to Proxima
Centauri, the nearest star.
- Barring any serious spacecraft subsystem failures, the Voyagers
may survive until the early twenty-first century, when diminishing
power and hydrazine levels will prevent further operation. Were
it not for these dwindling consumables and the possibility of
losing lock on the faint Sun, our tracking antennas could continue
to "talk" with the Voyagers for another century or two!
Excerpt from the Encyclopedia Britannica without permission.